Heat transfer method

ABSTRACT

The invention relates to a heat transfer method using ternary compositions containing 2,3,3,3-tetrafluoropropene, 1,1-difluoroethane and difluoromethane, said compositions being especially interesting as a heat transfer fluid in compression refrigeration systems comprising exchangers operation in counterflow mode or in split flow mode with counterflow tendency.

The present invention relates to the use of ternary compositions of 2,3,3,3-tetrafluoropropene as heat transfer fluids.

The problems posed by substances with ozone depletion potential (ODP) were discussed in Montreal, where the protocol was signed requiring a reduction of the production and use of chlorofluorocarbons (CFCs). Amendments were made to this protocol, which imposed abandonment of CFCs, and extended the regulations to cover other products, including hydrochloro-fluorocarbons (HCFCs).

The refrigeration and air conditioning industry has made a considerable investment in the replacement of these refrigerants, which is what led to the marketing of hydrofluorocarbons (HFCs).

The (hydro)chlorofluorocarbons used as expanding agents or solvents have also been replaced with HFCs.

In the automobile industry, the systems for air conditioning of vehicles marketed in many countries have changed over from a chlorofluorocarbon refrigerant (CFC-12) to a hydrofluorocarbon refrigerant (1,1,1,2-tetrafluoroethane: HFC-134a), which is less harmful to the ozone layer. However, with regard to the objectives established by the Kyoto protocol, HFC-134a (GWP=1300) is considered to have a high warming power. A fluid's contribution to the greenhouse effect is quantified by a criterion, GWP (Global Warming Potential), which summarizes the warming power, taking a reference value of 1 for carbon dioxide.

Carbon dioxide, being nontoxic, nonflammable and having a very low GWP, has been proposed as refrigerant for air conditioning systems, replacing HFC-134a. However, the use of carbon dioxide has several drawbacks, notably connected with the very high pressure for application as refrigerant in the existing equipment and technologies.

Moreover, the mixture R-404A consisting of 44 wt. % of pentafluoroethane, 52 wt. % of trifluoroethane and 4 wt. % of HFC-134a is widely used as fluid for refrigeration of large areas (supermarkets) and in refrigerated transport. However, this mixture has a GWP of 3900. The mixture R-4070, consisting of 52 wt. % of HFC-134a, 25 wt. % of pentafluoroethane and 23 wt. % of difluoromethane, is used as heat transfer fluid in air conditioning and heat pumps. However, this mixture has a GWP of 1800.

Document JP 4110388 describes the use of hydrofluoropropenes of formula C₃H_(m)F_(n), with m, representing an integer between 1 and 5 inclusive and m+n=6, as heat transfer fluids, in particular tetrafluoropropene and trifluoropropene.

Document WO2004/037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, notably pentafluoropropene and tetrafluoropropene, preferably having a GWP of at most 150, as heat transfer fluids.

Document WO 2005/105947 teaches the addition to tetrafluoropropene, preferably 1,3,3,3-tetrafluoropropene, of a co-blowing agent such as difluoromethane, pentafluoroethane, tetrafluoroethane, difluoroethane, heptafluoropropane, hexafluoropropane, pentafluoropropane, pentafluorobutane, water and carbon dioxide.

Document WO 2006/094303 discloses an azeotropic composition containing 7.4 wt. % of 2,3,3,3-tetrafluoropropene (1234yf) and 92.6 wt. % of difluoromethane (HFC-32). This document also discloses an azeotropic composition containing 91 wt. % of 2,3,3,3-tetrafluoropropene and 9 wt. % of difluoroethane (HFC-152a).

A heat exchanger is a device enabling thermal energy to be transferred from one fluid to another, without mixing them. The thermal flux passes through the exchange surface that separates the fluids. This method is most often used for cooling or heating a liquid or a gas that it is impossible to cool or heat directly.

In compression systems, heat exchange between the refrigerant and the heat sources is effected via heat-transfer fluids. These heat-transfer fluids are in the gaseous state (the air in air conditioning and direct-expansion refrigeration), liquid (the water in domestic heat pumps, glycol solution) or two-phase.

There are various transfer modes:

-   -   the two fluids are arranged in parallel and go in the same         sense: co-current mode (antimethodical);     -   the two fluids are arranged in parallel but go in the opposite         sense: countercurrent mode (methodical);     -   the two fluids are positioned perpendicularly: crossed-current         mode. Crossed-current can have a co-current or countercurrent         tendency;     -   one of the two fluids makes a U-turn in a wider pipeline, which         the second fluid passes through. This configuration is         comparable to a co-current exchanger over half its length, and         to a countercurrent exchanger for the other half: pin-head mode.

The applicant has now discovered that ternary compositions of 2,3,3,3-tetrafluoropropene, 1,1-difluoroethane and difluoromethane are particularly interesting as heat transfer fluid in compression-type refrigeration systems with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency.

Thus, these compositions can be used as heat transfer fluid in heat pumps, optionally reversible, in air conditioning, industrial air conditioning (paper, rooms for servers), in mobile domestic air conditioning, in domestic refrigeration and freezing, in low- and medium-temperature refrigeration and refrigeration of refrigerated vehicles employing compression systems with exchangers in countercurrent mode or in crossed-current mode with countercurrent tendency.

These compositions have both a zero ODP and a GWP below that of existing heat transfer fluids such as R-404A or R-407C. Moreover, their performance (COP: coefficient of performance, defined as the useful power delivered by the system over the power input or consumption of the system; and CAP: volumetric capacity (kJ/m³)) are greater than those of existing heat transfer fluids such as R-404A or R-407C.

The compositions used as heat transfer fluid in the present invention have a critical temperature above 93° C. (the critical temperature of R-404A is 72° C.). These compositions can be used in heat pumps to supply heat at temperatures up to 65° C. but also at higher temperatures up to 90° C. (temperature range where R-404A cannot be used).

The compositions used as heat transfer fluid in the present invention have pressures at the condenser lower than the pressures of R-404A as well as lower compression ratios. These compositions can use the same compressor technology used by R-404A. The compositions used as heat transfer fluid in the present invention have saturated vapor densities less than the saturated vapor density of R-404A. The volumetric capacities given by these compositions are equivalent to or greater than the volumetric capacity of R404A (between 97 and 110%). Owing to these properties, these compositions operate with smaller pipeline diameters and therefore less head loss in the vapor pipelines, which increases the performance of the installations.

The present invention therefore relates to the use of ternary compositions of 2,3,3,3-tetrafluoropropene, 1,1-difluoroethane and difluoromethane that are particularly interesting as heat transfer fluid in compression-type refrigeration systems with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency.

Preferably, the compositions used in the present invention contain essentially from 20 to 80 wt. % of 2,3,3,3-tetrafluoropropene and from 15 to 40 wt. % of difluoromethane and from 5 to 40 wt. % of 1,1-difluoroethane.

Advantageously, the compositions used contain essentially from 20 to 70 wt. % of 2,3,3,3-tetrafluoropropene and from 20 to 40 wt. % of difluoromethane and from 10 to 40 wt. % of difluoroethane.

The compositions that are particularly preferred contain essentially from 35 to 70 wt. % of 2,3,3,3-tetrafluoropropene from 20 to 25 wt. % of difluoromethane and from 10 to 40 wt. % of 1,1-difluoroethane.

The compositions used in the present invention can be stabilized. The stabilizer represents at most 5 wt. % relative to the total composition.

As stabilizers, we may notably mention nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2,6-di-tert-butyl-4-methylphenol, epoxides (alkyl optionally fluorinated or perfluorinated or alkenyl or aromatic epoxides) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether, butylphenylglycidyl ether, phosphites, phosphates, phosphonates, thiols and lactones.

Another object of the present invention relates to a method of heat transfer in which ternary compositions of 2,3,3,3-tetrafluoropropene, 1,1-difluoroethane and difluoromethane are used, which are particularly interesting as heat transfer fluid in compression-type refrigeration systems with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency.

The method according to the present invention can be employed in the presence of lubricants such as mineral oil, alkylbenzene, polyalkylene glycol and polyvinyl ether.

The compositions used in the present invention are suitable for replacing R-404A in refrigeration and/or R-407C in air conditioning and heat pumps in existing installations.

EXPERIMENTAL SECTION Tools for Calculation

The RK-Soave equation is used for calculating the densities, enthalpies, entropies and data for liquid-vapor equilibrium of the mixtures. To use this equation it is necessary to know the properties of the pure substances used in the mixtures in question as well as the coefficients of interaction for each binary mixture. The data required for each pure substance are: boiling point, critical temperature and pressure, curve of pressure as a function of temperature from the boiling point up to the critical point, saturated liquid density and saturated vapor density as a function of temperature.

HFC-32, HFC-152a:

The data for these products are published in ASHRAE Handbook 2005 chapter 20, and are also available using Refrop (software developed by NIST for calculating the properties of refrigerants).

HFO-1234yf:

The data for the temperature-pressure curve of HFO-1234yf are measured by the static method. The critical temperature and pressure are measured with a C80 calorimeter marketed by Setaram. The densities at saturation as a function of temperature are measured by the technology of the vibrating-tube densimeter developed by the laboratories of the Ecole des Mines de Paris.

Coefficient of Interaction of the Binary Mixtures

The RK-Soave equation uses coefficients of binary interaction for representing the behavior of the products in mixtures. The coefficients are calculated as a function of experimental data for liquid-vapor equilibrium.

The technique used for the measurements of liquid-vapor equilibrium is the static analytical cell method. The equilibrium cell comprises a sapphire tube and is equipped with two ROLSITM electromagnetic samplers. It is immersed in a cryothermostat bath (HUBER HS40). Magnetic stirring driven by a field rotating at variable speed is used to accelerate the attainment of equilibrium. The samples are analyzed by gas chromatography (HP5890 series II) using a catharometer (TCD).

HFC-32/HFO-1234yf, HFC-152a/HFO-1234yf:

The measurements of liquid-vapor equilibrium on the HFC-32/HFO-1234yf binary mixture are performed for the following isotherms: −10° C., 30° C. and 70° C.

The measurements of liquid-vapor equilibrium on the HFC-152a/HFO-1234yf binary mixture are performed for the following isotherms: 10° C.

HFC-32/HF0-152a:

The data for liquid-vapor equilibrium for the HFC-152a/HFC-32 binary mixture are available using Refprop. Two isotherms (−20° C. and 20° C.) and two isobars (1 bar and 25 bar) are used for calculating the coefficients of interaction for this binary mixture.

Compression System

Consider a compression system equipped with an evaporator and countercurrent condenser, a screw compressor and a pressure reducing valve.

The system operates with 15° C. of superheating and 5° C. of supercooling. The minimum temperature difference between secondary fluid and the refrigerant is considered to be of the order of 5° C.

The isentropic efficiency of the compressors is a function of the compression ratio. This efficiency is calculated from the following equation:

$\begin{matrix} {\eta_{isen} = {a - {b\left( {\tau - c} \right)}^{2} - {\frac{d}{\tau - e}.}}} & (1) \end{matrix}$

For a screw compressor, constants a, b, c, d and e in equation (1) of isentropic efficiency are calculated using the standard data published in the Handbook “Handbook of air conditioning and refrigeration, page 11.52”. The % CAP is the percentage of the ratio of the volumetric capacity supplied by each product to the capacity of R-404A.

The coefficient of performance (COP) is defined as the useful power delivered by the system over the power input or consumption of the system.

The Lorenz coefficient of performance (COPLorenz) is a reference coefficient of performance. It is a function of temperature and is used for comparing the COPs of different fluids.

The Lorenz coefficient of performance is defined as follows:

(The temperatures T are in K)

T _(mean) ^(condenser) =T _(inlet) ^(condenser) −T _(outlet) ^(condenser)  (2)

T _(mean) ^(evaporator) =T _(outlet) ^(evaporator) −T _(inlet) ^(evaporator)  (3)

The Lorenz COP in the case of air conditioning and refrigeration is:

$\begin{matrix} {{COPlorenz} = \frac{T_{mean}^{evaporator}}{T_{mean}^{condenser} - T_{mean}^{evaporator}}} & (4) \end{matrix}$

The Lorenz COP in the case of heating is:

$\begin{matrix} {{COPlorenz} = \frac{T_{mean}^{condenser}}{T_{mean}^{condenser} - T_{mean}^{evaporator}}} & (5) \end{matrix}$

For each composition, the coefficient of performance of the Lorenz cycle is calculated as a function of the corresponding temperatures.

% COP/COPLorenz is the ratio of the COP of the system to the COP of the corresponding Lorenz cycle.

Results in Heating Mode

In heating mode, the compression system operates between an inlet temperature of the refrigerant at the evaporator of −5° C. and an inlet temperature of the refrigerant at the condenser of 50° C. The system supplies heat at 45° C.

The performance of the compositions according to the invention in the operating conditions in heating mode are given in table 1. The values of the constituents (HFO-1234yf, HFC-32, HFC-152a) for each composition are given as percentage by weight.

TABLE 1 Temp outlet Temp outlet T outlet evap P cond P Ratio efficiency % COP/ evap (° C.) comp (° C.) cond (° C.) (bar) (bar) (w/w) Shift comp % CAP COPLorenz R404A −5 77 50 5.2 23.0 4.4 0.38 79.7 100 57.7 HFO- HFC- HFC- 1234yf 32 152a 70 20 10 0 81 43 4.2 17.3 4.1 4.86 80.7 97 65.8 60 25 15 0 85 43 4.4 18.1 4.1 5.02 80.7 104 65.9 50 25 25 0 88 43 4.2 17.7 4.2 4.98 80.4 102 66.6 35 25 40 0 92 43 3.9 16.9 4.3 5.18 80.1 100 67.6

Results for Cooling, Mode or Air Conditioning

In cooling mode, the compression system operates between an inlet temperature of the refrigerant at the evaporator of −5° C. and an inlet temperature of the refrigerant at the condenser of 50° C. The system supplies cold at 0° C. 0.10 The performance of the compositions according to the invention in the operating conditions in cooling mode is shown in table 2. The values of the constituents (HFO-1234yf, HFC-32, HFC-152a) for each composition are given as percentage by weight.

TABLE 2 Temp outlet Temp outlet T outlet evap P cond P Ratio efficiency % COP/ evap (° C.) comp (° C.) cond (° C.) (BAR) (bar) (w/w) Shift comp % CAP COPLorenz R404A −5 77 50 5.2 23.0 4.4 0.38 79.7 100 47.9 HFO- HFC- 1234yf HFC-32 152a 70 20 10 0 81 43 4.2 17.3 4.1 4.86 80.7 105 57.8 65 20 15 0 82 43 4.1 17.1 4.2 4.68 80.6 104 58.3 60 25 15 0 85 43 4.4 18.1 4.1 5.02 80.7 113 58.2 55 20 25 0 85 43 3.9 16.7 4.2 4.52 80.3 104 59.0 50 25 25 0 88 43 4.2 17.7 4.2 4.98 80.4 112 59.2 40 20 40 0 89 43 3.7 16.1 4.4 4.58 80.0 103 60.3 35 25 40 0 92 43 3.9 16.9 4.3 5.18 80.1 110 60.5 

1. (canceled)
 2. The heat transfer system as claimed in claim 6, characterized in that the ternary composition consists essentially of from 20 to 80 wt. % of 2,3,3,3-tetrafluoropropene and from 15 to 40 wt. % of difluoromethane and from 5 to 40 wt. % of difluoroethane.
 3. The heat transfer system as claimed in claim 6, characterized in that the ternary composition consists essentially of from 20 to 70 wt. % of 2,3,3,3-tetrafluoropropene and from 20 to 40 wt. % of difluoromethane and from 10 to 40 wt. % of difluoroethane.
 4. (canceled)
 5. The heat transfer system as claimed in claim 6, characterized in that the ternary composition is stabilized.
 6. A heat transfer system comprising a compression-type refrigeration system with exchangers operating in countercurrent mode or in crossed-current mode with countercurrent tendency and a refrigerant comprising a ternary composition of 2,3,3,3-tetrafluoropropene, 1,1-difluoroethane and difluoromethane.
 7. The heat transfer system as claimed in claim 6, characterized in that the ternary composition consists essentially of from 35 to 70 wt. % of 2,3,3,3-tetrafluoropropene and from 20 to 25 wt. % of difluoromethane and from 10 to 40 wt. % of difluoroethane.
 8. The heat transfer system as claimed in claim 6, characterized in that further comprises a lubricant. 